Bottom hole assemblies are part of the drill string. Specifically, a bottom hole assembly typically refers to the lower part of the drill string, extending from a drill bit to a drill pipe. In some configurations, a bottom hole assembly may include a reamer. A reamer may follow the drill bit down the hole, and may serve to increase the diameter of the hole initially drilled by the drill bit.
Conventional reamers have been designed to match the drill bits with which they are paired. Generally, this matching includes physically matching the configuration of cutters disposed on a reamer, in terms of size, diameter, and/or back rakes with the cutters used on the matched drill bit, and/or attempting to match operating characteristics of the reamer with operating characteristics of the drill bit so that the reamer and the drill bit will react the same to changes in rotary speed and/or weight on bit. As used here, the term “match” means pairing and working together to exhibit predictable behaviors and outcomes.
During operation, however, the attempt to match operation characteristics may prove futile as the drill bit and the reamer proceed in series through different formations, experience wear at different rates and/or in different ways, and/or experience other phenomena that cause mis-matched operation. These sources of misalignment between the operation characteristics of the drill bit and the reamer may become sources of vibration, which, in addition to causing failures to bits and/or reamers, may also cause failures to much more expensive downhole tools, such as logging, imaging, and rotary steerable systems. In additions, these dynamic conditions can contribute to shorter and slower runs, which may in turn force multiple trips and increase operational costs. In hard and/or abrasive formations, and as well depths have gotten deeper, these failures have significant effects on project costs. To bring these costs in line, industry researchers have focused on solutions that will address these problems.